Which graphic card I should choose for my laptop for gaming?

I have a lenovo think pad E430
4 GB ram
Intel Core i5-3230M CPU @ 2.60GHz
Intel HD Graphics 4000
MS Windows 7 64-bit

You can't change your graphics card in your laptop.;/

I doubt you can change/add but if you are building Id say go with Nvidia or a good AMD, though most Nvidia arent that bad and the Nvidia physX is a nice addon